HL 8.1 Metabolism

Metabolism Metabolic pathways consist of chains and cycles of enzyme-catalyzed reactions. http://www.genome.jp/kegg/

Activation Energy

Competitive Inhibition Substrate and inhibitor are chemically very similar Inhibitor binds to the active site of the enzyme, prevents substrate from binding Example: Folic acid synthetase Folic acid synthetase is an enzyme in bacteria which normally produces folic acid (vitamin) from PABA Sulfanilamides (antibiotics) occupies the active site of folic acid synthetase; blocks access of PABA Bacteria die without folic acid

Non-competitive inhibition Substrate and inhibitor are not similar Inhibitor binds to the enzyme at different site than the active site The inhibitor changes the of the enzyme, causing slow enzyme activity Example: silver, Ag+ silver forms bonds with the -SH groups of cysteine, the amino acid which forms covalent disulfide bridges the disruption of disulfide bridges alters the tertiary structure of the enzyme, affecting its active site

End product inhibition When the end product is formed in excess, the excess products interact with enzymes at the beginning of the pathway  decrease enzyme activity Negative feedback = the rate of the process decreases as the concentration of the product increases. Example: Threonine to isoleucine (amino acids) Negative feedback: http://highered.mheducation.com/sites/9834092339/student_view0/chapter46/positive_and_negative_feedback.html

Distinguish between different types of inhibition Competitive inhibition: more substrate, greater rate of reaction Non competitive inhibition: prevents enzyme binding regardless of substrate concentration V = rate of reaction [S] = substrate concentration